Introduction

CoffeeScript code is not processed by browsers that work with JavaScript code. Therefore to be executed, CoffeeScript code has to be translated into JavaScript.
This operation is referred to as transpilation and the tools that perform it are called transpilers.

WebStorm supports integration with the coffee-script transpilation tool.
The tool translates CoffeeScript code into JavaScript and creates source maps
that set correspondence between lines in your CoffeeScript code and in the generated JavaScript code,
otherwise your breakpoints will not be recognised and processed correctly.

In WebStorm, transpiler configurations are called File Watchers.
For each supported transpiler, WebStorm provides a predefined File Watcher template.
Predefined File Watcher templates are available at the WebStorm level. To run a transpiler against your project files, you need to
create a project-specific File Watcher based on the relevant template, at least, specify the path to the transpiler to use on your machine.

In either installation mode, make sure that the parent folder of the CoffeeScript transpiler is added to the PATH variable.
This enables you to launch the transpiler from any folder.

WebStorm provides user interface both for global and project installation as well as supports installation through the command line.

Before you start

Download and install Node.js. The runtime environment is required for two reasons:

The CoffeeScript transpiler is started through Node.js.

NPM, which is a part of the runtime environment, is also the easiest way to download the CoffeeScript transpiler.

If you are going to use the command line mode, make sure the path to the parent folder of the Node.js executable file
and the path to the npm folder are added to the PATH variable.
This enables you to launch the CoffeeScript transpiler and npm from any folder.

Make sure the File Watchers plugin is enabled. The plugin is bundled with WebStorm and activated by default. If it is not,
enable the plugin. See Enabling and Disabling Plugins for details.

Installing the CoffeeScript transpiler globally

Global installation makes a transpiler available at the WebStorm level so it can be used in any WebStorm project.
Moreover, during installation the parent folder of the transpiler is automatically added to the PATH variable,
which enables you to launch the transpiler from any folder.
To install the transpiler globally, do one of the following:

Run the installation from the command line in the global mode:

Launch the embedded Terminal
by hovering your mouse pointer over in the lower left corner of WebStorm and choosing Terminal from the menu
(see Working with Embedded Local Terminal for details).

Switch to the directory where NPM is stored or define a PATH variable for it so it is available from any folder,
see Installing NodeJs.

Type the following command at the command line prompt:

npm install -g coffee-script

The -g key makes the transpiler run in the global mode.
Because the installation is performed through NPM, the CoffeeScript transpiler is installed in the npm folder.
Make sure this parent folder is added to the PATH variable. This enables you to launch the transpiler from any folder.

Run NPM from WebStorm using the Node.js and NPM page of the Settings dialog box.

Open the Settings / Preferences Dialog by pressing Ctrl+Alt+S or by choosing File | Settings for Windows and Linux or
WebStorm | Preferences for OS X,
and
click Node.js and NPM under Languages&Frameworks.

On the Node.js and NPM page that opens, the Packages area shows all the Node.js-dependent packages
that are currently installed on your computer, both at the global and at the project level.
Click .

In the Available Packages dialog box that opens, select the required package to install.

Select the Options check box and type -g in the text box next to it.

Optionally specify the product version and click Install Package to start installation.

Installing the CoffeeScript transpiler in a project

Installing a transpiler in a specific project restricts its use to this project.
To run project installation, do one of the following:

Run the installation from the command line:

Launch the embedded Terminal
by hovering your mouse pointer over in the lower left corner of WebStorm and choosing Terminal from the menu
(see Working with Embedded Local Terminal for details).

Switch to the project root folder and type the following command at the command line prompt:

npm install coffee-script

Run NPM from WebStorm using the Node.js and NPM page of the Settings dialog box.

Open the Settings / Preferences Dialog by pressing Ctrl+Alt+S or by choosing File | Settings for Windows and Linux or
WebStorm | Preferences for OS X,
and
click Node.js and NPM under Languages & Frameworks.

On the Node.js and NPM page that opens, the Packages area shows all the Node.js-dependent packages
that are currently installed on your computer, both at the global and at the project level.
Click .

In the Available Packages dialog box that opens, select the required package.

Optionally specify the product version and click Install Package to start installation.

Project level installation is helpful and reliable in template-based projects
of the type Node Boilerplate or Node.js Express, which already have the node_modules folder.
The latter is important because NPM installs the CoffeeScript transpiler
in a node_modules folder. If your project already contains such folder, the CoffeeScript transpiler is installed there.

Projects of other types or empty projects may not have a node_modules folder.
In this case npm goes upwards in the folder tree and installs the CoffeeScript transpiler
in the first detected node_modules folder. Keep in mind that this detected node_modules folder may be outside your current project root.

Finally, if no node_modules folder is detected in the folder tree either,
the folder is created right under the current project root and the CoffeeScript transpiler is installed there.

In either case, make sure that the parent folder of the CoffeeScript transpiler is added to the PATH variable.
This enables you to launch the transpiler from any folder.

Creating a File Watcher

WebStorm provides a common procedure and user interface for creating File Watchers of all types.
The only difference is in the predefined templates you choose in each case.

To start creating a File Watcher, open the Settings/Preferences dialog box by choosing
File | Settings for Windows and Linux or WebStorm | Preferences for OS X
on the main menu, and then click File Watchers under the Tools node.
The File Watchers page that opens, shows the list of File Watchers that are already configured in the project.

Click the Add button or press Alt+Insert
and choose the CoffeeScript predefined template from the pop-up list.
Your code will be translated to JavaScript and supplied with generated source maps.

In the Program text box, specify the path to the coffee.cmd file. Type the path manually or click the Browse button
and choose the file location in the dialog box that opens.

Examples of customizing the behaviour of a transpiler

Any transpiler is an external, third-party tool. Therefore the only way to influence a transpiler is pass arguments to it
just as if you were working in the command line mode. Below are two examples of customizing the default output location for the CoffeeScript transpiler.

Suppose, you have a project with the following folder structure:
By default, the generated files will be stored in the folder where the original file is. You can change this default location and have the generated files stored in the js folder.
Moreover, you can have them stored in a flat list or arranged in the folder structure that repeats the original structure under the app node.

To have all the generated files stored in the output js folder without retaining the original folder structure under the app folder:

Transpiling the CoffeeScript code

When you open a CoffeeScript file, WebStorm checks whether an applicable file watcher is available in the current project. If such file watcher is configured but disabled,
WebStorm displays a pop-up window that informs you about the configured file watcher and suggests to enable it.

If an applicable file watcher is configured and enabled in the current project, WebStorm starts it automatically
upon the event specified in the New Watcher dialog.

If the Immediate file synchronization check box is selected, the File Watcher is invoked as soon as any changes are made to the source code.

If the Immediate file synchronization check box is cleared,
the File Watcher is started upon save (File | Save All, Ctrl+S) or when you move focus from WebStorm
(upon frame deactivation).

The transpiler stores the generated output in a separate file. The file has the name of the source CoffeeScript file and the extension js or js.map
depending on the transpiler type. The location of the generated files is defined in the Output paths to refresh text box
of the New Watcher dialog. Based on this setting, WebStorm detects the transpiler output.
However, in the Project Tree, they are shown under the source .coffee file
which is now displayed as a node.

Previewing the transpilation results without running a transpiler

WebStorm can perform static analyses of your CoffeeScript code without actually running a transpiler
and display the predicted transpilation output in the dedicated read-only viewer.

Open the desired CoffeeScript file in the editor, and right-click the editor background.

On the context menu, choose Preview Compiled CoffeeScript File.
The preview is opened in the dedicated read-only viewer: the left-hand pane shows the original CoffeeScript source code
and the right-hand pane shows the JavaScript code that will be generated by the transpiler when it runs.